1. Field of the Invention
The present invention relates to a structure and device as well as a method applied to an optical system that modulates light from a light source through a plurality of optical modulation elements, and more particularly, to an optical propagation structure and optical display device of an optical system preferable for improving imaging accuracy and highly accurate modulation, a light propagation method of an optical system and a display method of an optical display device.
Priority is claimed on Japanese Patent Application No. 2003-427208 filed Dec. 24, 2003, and Japanese Patent Application No. 2004-299284 filed Oct. 13, 2004, the content of which are incorporated herein by reference.
2. Description of the Related Art
Dramatic improvements have been made in recent years in the image quality of liquid cry displays (LCD), EL, plasma displays, cathode ray tubes (CRT), projectors and other optical display devices, and performance with respect to resolution and color gamut are nearly comparable to human vision characteristics. However, the reproduction range of luminance dynamic range is at best about 1 to 102 nit, while the number of gradations is typically 8 bits. On the other hand, the luminance dynamic range that can be visualized all at once by human vision is about 10−2 to 10−4 nit, while luminance discrimination ability is about 0.2 nit, and when this is converted into a number of gradations, it is said to be equivalent to 12 bits. When considering the displayed images of current optical display devices in terms of these vision characteristics, the narrowness of the luminance dynamic range is conspicuous, and due to a lack of gradation of shadowed and highlighted areas, displayed images appear to lack realism and impact.
In addition, in the field of computer graphics (CG) used in movies and video games, there is a growing trend to pursue greater depiction reality by giving a luminance dynamic range and number of gradations that approach human vision to display data (referred to as high dynamic range (HDR) display data). However, due to the lack of performance of optical display devices that display that data, there is the problem in which CG images are unable to adequately demonstrate their inherent expressive capabilities.
Moreover, 16-bit color space is scheduled to be employed in next-generation operating systems (OS), resulting in a dramatic increase in the luminance dynamic range and number of gradations as compared with current 8-bit color space. Consequently, it is desirable to realize optical display devices capable of taking advantage of 16-bit color space.
Among optical display devices, liquid crystal projectors, DLP projectors and other projection-type display devices are capable of large-screen display, and are effective devices in terms of reproducing reality and impact of displayed images. In this field, the following proposals have been made to solve the aforementioned problems.
Technology for a high dynamic range projection-type display device is disclosed in, for example, Patent Document 1 (Japanese Unexamined Patent Application, First Publication No. 9-116840). This display device is provided with a light source, a first optical modulation element that modulates the luminance of the entire wavelength region of the light, and a second optical modulation element that modulates luminance of the wavelength region for each wavelength region of three primary colors of red, green and blue (RGB) within the wavelength region of the light. In this device, light from the light source forms a desired luminance distribution by modulating with the first optical modulation element, the optical image is then transmitted to the pixel surfaces of the second optical modulation element to modulate the color, after which the secondary modulated light is projected. Each pixel of the first optical modulation element and second optical modulation element is individually controlled based on a first control value and second control value, respectively, that are determined from HDR display data. Transmitting modulation elements having a pixel structure or segment structure that allows independent control of the transmission factor and are capable of controlling the two dimensional distribution of transmission factor are used for the optical modulation elements. A typical example of this is a liquid crystal light valve. In addition, a reflecting modulation element may be used instead of a transmitting modulation element, and a typical example of this is a digital micromirror device (DMD).
The following considers the case of using an optical modulation element having a dark display transmission factor of 0.2% and a bright display transmission factor of 60%. In the case of the optical modulation element alone, the luminance dynamic range is 60/0.2=300. Since the aforementioned projection-type display device of the prior art is equivalent to optically arranging optical modulation elements having a luminance dynamic range of 300 in series, a luminance dynamic range of 300×300=90,000 can be realized. In addition, since the same approach is valid for the number of gradations, a number of gradations in excess of 8 bits can be obtained by optically arranging optical modulation elements having a gradation of 8 bits in series.
In addition, another example of a projection-type display device that realizes a high luminance dynamic range is known that is disclosed in, for example, Patent Document 2 (Japanese Unexamined Patent Application, First Publication No. 2001-100689).
The invention described in Patent Document 2 is provided with a light source, a first optical modulation element, an optical isolator that divides light from the first optical modulation element into the three colors of red, green and blue (RGB), a plurality of second optical modulation elements into which the light divided with the optical isolator respectively enters, and a cross prism that synthesizes the light from each of the second optical modulation elements, wherein light from the light source is modulated through the first and second optical modulation elements to display an image. In the invention described in Patent Document 2, the first optical modulation element forms an image on the second optical modulation elements through the use of optical lenses that compose an illumination optical system.
However, in the invention described in Patent Document 1, even though an optical isolator is provided between the first and second optical modulation elements and the first and second optical modulation elements are separated from each other, since there is no lens or other image-forming means between them, there was the problem of it being difficult to accurately transmit the optical image of the first optical modulation element to the pixel surfaces of the second optical modulation element. In addition, in the invention described in Patent Document 2, although image-forming accuracy can be improved to a certain extent if that having high accuracy is used for the lenses, mirrors and other optical components that compose the illumination optical system, there was the problem of composing with highly accurate optical components leading to increased costs.
FIG. 21 is a drawing showing the constitution of a light path of a first optical modulation element and a second optical modulation element in a projection-type display device described in Patent Document 2. Furthermore, although mirrors and other optical elements are also arranged in an actual light path, these optical elements are omitted from FIG. 21 in order to facilitate understanding of the following explanation.
In the optical system of FIG. 21, a first optical modulation element 130 for modulating luminance is arranged on the side of the light source with fly eye lenses 112a and 112b in between and second optical modulation element 140 for modulating color is arranged on the opposite side of the light source with fly eye lenses 112a and 112b in between. In this optical system, the optical image of each element lens that composes fly eye lens 112a close to first optical modulation element 130 is formed on the pixel surfaces of second optical modulation element 140. Consequently, in order to obtain a desired luminance distribution, this distribution of luminance must be formed for each element lens. However, fly eye lenses 112a and 112b are optical elements used for the purpose of making the luminance distribution uniform, and the number of element lenses is preferably large to achieve this objective. This being the case, the size of each lens is inevitably smaller than the size of second optical modulation element 140. More specifically, lenses that are one-third to one-fifth the size of second optical modulation element 140 are used. When considering that the pixels of second optical modulation element 140 and the pixels of first optical modulation element 130 are made to correspond on a 1:1 basis, the pixel density of first optical modulation element 130 is required to be three to five times the pixel density of second optical modulation element 140. However, current optical modulation elements (e.g., liquid crystal light valves) already have pixel densities that approach the upper limit of hyperfine processing technology in order to achieve higher resolution, and in consideration of this point, it would be difficult to attempt to realize a pixel density that is three to five times greater in first optical modulation element 130. Thus, the accuracy of the lance distribution capable of being formed with first optical modulation element 130 is forced to be three to five times cruder than the pixel density of second optical modulation element 140. Moreover, since optical images of each element lens are formed on the pixel surfaces of second optical modulation element 140 with only two lenses consisting of fly eye lens 112b and converging lens 12d located far from first optical modulation element 130, aberration is unable to be adequately corrected which inevitably results in considerable blurring of the images. Accordingly, there was the problem of it being difficult accurately adjust luminance.
Therefore, in consideration of the unresolved problems of the prior art as described above, the object of the present invention is to provide a light propagation structure and optical display device of an optical system preferable for improving image-forming accuracy and highly accurate modulation without increasing costs, along with a light propagation method of an optical system and a display method of an optical display device.